In the steel mills and related metallurgical industries, it is customary to form a basic metal shape often called a slab, billet or bloom which is ultimately worked into another form or shape before it leaves the mill. In order to rework the basic shape, it is frequently necessary to reheat the shape in order to make it more malleable during the reworking procedure. A typical metallurgical furnace includes a complex network of vertical and horizontal water-cooled pipes which support an additional network of horizontal circular water-cooled skid pipes which have wear-resistant metal strips along their upper surfaces over which the shapes, in the case of a pusher-type furnace, can be pushed through the furnace during the reheat procedure.
During furnace operations, the movement of the metal shapes along the skid pipes causes large amounts of stress and bending forces to be applied directly to the skid pipe. These forces in combination with the high temperature environment frequently cause the failure or serious degradation of portions of the skid pipe system within the furnace thereby necessitating the shutdown of the furnace for repairs.
The skid pipe, which conventionally includes a circular water-cooled pipe, a refractory around the pipe and some sort of a wear-resistant strip or skid secured to the top of the pipe, must simultaneously provide sufficient support for the metal shapes being pushed across the skid, sufficient resistance to vibrations and coupling effects or moment forces, permit a sufficient flow of cooled water through it to maintain the skid pipe system at a sufficiently low operating temperature, and retain a refractory around the skid rail, excepting the actual skid itself, which reduces heat loss from the furnace into the pipe.
The industry today generally utilizes a skid pipe comprising a circular water-cooled pipe, a metal skid which is welded to or otherwise attached to the top of the circular pipe and a heavy pre-fired ceramic brick refractory which encompasses a majority of the water-cooled pipe. The industry has unsuccessfully attempted to secure the heavy pre-fired ceramic brick around the circular pipe by welding metal studs to the pipe which project outwardly of the pipe into corresponding recesses within the refractory. The procedure for welding the studs to the pipe is tedious and expensive, while at the same time requiring a vast expenditure of labor in order to apply the refractory to the water-cooled skid pipe. High temperature slag tends to collect on the upper portion of the water-cooled pipe as the slag falls or is scraped from the overhead metal shape. Hence, the slag encroaches into the seams between the refractory and the pipe and quickly causes the refractory to fall from the skid rail system. Furthermore, the vibrations caused by the passing of the metal shapes over the skid rails is transmitted along and throughout the skid pipe system which causes the brittle ceramic tiles or pre-fired ceramic brick to fracture and/or to break the metal studs from the pipe, the result in any event being that the water-cooled skid pipe quickly becomes uninsulated and the source of a tremendous energy loss in the furnace.
The use of refractory cements to reinforce and protect the seams or margins between the sections of a refractory or between the refractory and the water-cooled pipe have further proved less than desirable inasmuch as the vibrations cause the brittle cement to fracture and fall from the skid rail in a brief period of time.
Although various shapes of the water-cooled skid pipe have been tested and used, such as, for example, elliptically-shaped, triangular-shaped, teardrop-shaped skid rails and the like, these shapes have been utilized in order to reduce the "shadow effect." The shadow effect is a phenomenon in the metallurgical reheat furnace which results from those portions of the metal shapes which are in contact with the cooler metal skid on the skid pipe which in turn draws a disproportionate amount of heat from the corresponding surface of the metal shape and deposits that heat into the cooling water within. The various shapes of water-cooled pipe which have been utilized in skid pipe systems, however, have in no way resolved the fundamental problem encountered; that is, increasing the ability of the skid pipe to withstand the vibrations, moments and forces exerted upon it during operation and the preventing of slag from migrating into the seams between the skid pipe and insulator thereby causing the the surrounding refractory quickly to be parted from the water-cooled skid pipe thereby permitting unacceptable amount of heat to be transferred into the flowing water and forever lost outside the furnace.